The present invention relates to the construction of an altitude compensation valve assembly for use in a fluid operated system.
The U.S. Pat. No. 3,456,632, patented on July 22, 1969, for example, discloses an altitude compensation valve assembly operatively coupled to a carburetor throttle valve for controlling the throttle valve opening during high manifold vacuum low pressure resulting from variation in altitude of the internal combustion engine. The altitude compensation valve assembly disclosed in this U.S. patent comprises a housing having first and second working chambers, the first working chamber accommodating therein a sealed evacuated bellows and being in communication with the engine intake manifold downstream of the throttle valve. The bellows used therein is made of resilient metallic material and, therefore, tends to expand axially by the action of the resiliency of the metallic material for the bellows. A wall dividing the interior of the housing into the first and second working chambers has a valve stem extending therethrough, said valve stem having one end positioned adjacent an end plate secured to the bellows, the other end of which valve stem carries a valve member normally closing a passage defined in the wall around the valve stem and communicating between the first and second working chambers when the valve is opened. This altitude compensation valve assembly is so designed that, when the manifold pressure in the first working chamber falls below a predetermined value during, for example, deceleration of the internal combustion engine, the bellows expands with the end plate pushing the valve stem, thereby causing the valve member to open the passage. As the passage between the first and second working chambers is opened, the manifold pressure is also developed in the second working chamber and, therefore, an operating rod having one end coupled to the throttle valve and the other end situated within the second working chamber is drawn against a spring biasing force to open the throttle valve. On the other hand, as the manifold pressure increases over the predetermined value, the altitude compensation valve assembly operates in a reverse manner.
While the altitude compensation valve assembly of the above mentioned U.S. patent is satisfactory in that the position of the throttle valve of the carburetor can be adjusted to control the quantity of combustible mixture admitted to the combustion chamber of the engine during deceleration regardless of the altitude or the environment in which the engine is operated, an apparent disadvantage has been found in that it requires a precise adjustment of the bellows in consideration of the equilibrium of the pressure in the first working chamber, the internal pressure in the bellows and the resiliency of the metallic material for the bellows. Moreover, it has been found that, because of the construction of the valve assembly requiring a mechanical linkage between the valve assembly and a device whose operation or position is to be controlled thereby, it has a limited range of application.